I went and looked on UESP for you and found this link for you: http://www.gamesas.com/topic/1313851-complete-character-design-freedom-damage-resist-caps-and-ridiculous-damage-thread-7/page__st__90__p__19786622#entry19786622
One guy says 4/5 perks or a 40% enchant hits the cap.
Thanks for that. Trust me I am not lazy, I did check the block skill on UESP and the discussion tab for that page, but I didn't know people discussed game mechanics on the forums, I thought that was all reserved for the wiki.
I'm still a little fuzzy on your info though, so you're saying that with 100 block skill and 4/5 in the block perk you're capped? I wish Beth would be more careful so people don't end up having to waste perks like that.
If I remember correctly, in regards to blocking and magic/elemental resistances, it was said that the cap was 85% and anything on your gear or perks, after that, won't go past that amount. Otherwise, 100% in Frost, Fire, Shock and Damage would make you unbreakable.
So this info is a bit different to the above poster, you're saying 85% which would be a combination of gear and perks, and his info suggest the block cap would be much easier to reach. Wouldn't need enchanted gear to hit it.